Is NO^-NO Paramagnetic or Diamagnetic?

1 Answer
Apr 7, 2016

The MO diagram for "NO"NO is as follows (Miessler et al., Answer Key):

(The original was this; I added the orbital depictions and symmetry labels.)

Quick overview of what the labels correspond to what MOs:

  • 1a_11a1 is the sigma_(2s)σ2s bonding MO.
  • 2a_12a1 is the sigma_(2s)^"*"σ*2s antibonding MO.
  • 1b_11b1 is the pi_(2p_x)π2px bonding MO.
  • 1b_21b2 is the pi_(2p_y)π2py bonding MO.
  • 3a_13a1 is the sigma_(2p_z)σ2pz bonding MO, but it's relatively nonbonding with respect to oxygen.
  • 2b_12b1 is the pi_(2p_x)^"*"π*2px antibonding MO.
  • 2b_22b2 is the pi_(2p_y)^"*"π*2py antibonding MO.
  • 4a_14a1 is the sigma_(2p_z)^"*"σ*2pz antibonding MO.

Since this is "NO"NO, if you add an electron to get to "NO"^(-)NO, you add it into the 2b_22b2 orbital, which is the \mathbf(pi_(2p_y)^"*") antibonding MO.

That increases its paramagnetic properties, as there exist two unpaired electrons now instead of just one.

CHALLENGE: What does that do to the N-O pi bond? Does it weaken or strengthen it? (Hint: Consider the bond order). What about NO^(+)? Is that diamagnetic, and how do you know?